Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called “perpendicular” recording media have been found to be superior to the more conventional “longitudinal” media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
Efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (as compared with the magnetic recording layer), magnetically “soft” underlayer (“SUL”) layer, i.e., a magnetic layer having a relatively low coercivity of about 1 kOe or below, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the magnetically “hard” recording layer having relatively high coercivity of several kOe, e.g., of a cobalt-based alloy (e.g., a Co—Cr alloy such as CoCrPtB) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer.
A typical conventional perpendicular recording system 10 utilizing a vertically oriented magnetic medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 2A, 3, 4, 5, 11, and 12, respectively, indicate a non-magnetic substrate, an adhesion layer (optional), a soft magnetic underlayer, at least one non-magnetic interlayer, at least one perpendicular hard magnetic recording layer, a protective overcoat layer, and a lubricant topcoat layer. Reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of a single-pole magnetic transducer head 6. The relatively thin interlayer 4 (also referred to as an “intermediate” layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 3 and the at least one hard recording layer 5 and (2) promote desired microstructural and magnetic properties of the at least one hard recording layer.
As shown by the arrows in the figure indicating the path of the magnetic flux φ, flux φ is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through the at least one vertically oriented, hard magnetic recording layer 5 in the region above single pole 7, entering and travelling along soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through the at least one perpendicular hard magnetic recording layer 5 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of polycrystalline layers 4 and 5 of the layer stack constituting medium 1. Since magnetically hard main recording layer 5 is epitaxially formed on interlayer 4, the grains of each polycrystalline layer are of substantially the same width (as measured in a horizontal direction) and in vertical registry (i.e., vertically “correlated” or aligned). Completing the layer stack is a protective overcoat layer 11, such as of a diamond-like carbon (DLC), formed over hard magnetic layer 5, and a lubricant topcoat layer 12, such as of a perfluoropolyethylene material, formed over the protective overcoat layer.
Substrate 2 is typically disk-shaped and comprised of a non-magnetic material capable of withstanding the elevated temperatures typically required for deposition thereon of the various constituent layers of the media, as described supra. Typical substrates, therefore, include non-magnetic metals or alloys, e.g., Al or Al-based alloys, such as Al—Mg having an Ni—P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic material, or a composite or laminate of these materials. Optional adhesion layer 2A, if present, may comprise an up to about 30 Å thick layer of a material such as Ti or a Ti alloy or Cr or a Cr alloy; soft magnetic underlayer 3 is typically comprised of an about 500 to about 4,000 Å thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFeZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeCoB, FeCoC, etc.; interlayer 4 typically comprises an up to about 300 Å thick layer or layers of non-magnetic material(s), such as Ru, TiCr, Ru/CoCr37Pt6, RuCr/CoCrPt, etc.; and the at least one hard magnetic layer 5 is typically comprised of an about 100 to about 250 Å thick layer(s) of Co-based alloy(s) including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, B, and Pd, iron nitrides or oxides, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 Å thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, Pt, W, and Fe, and each of the alternating thin, non-magnetic layers of Pd or Pt is up to about 10 Å thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
The continuing trend toward the manufacture of very low cost (e.g., <$500) personal computers (PCs) necessitates a reduction in the cost of hard disk drives utilized in such computers, while at the same time, the escalating requirements for increased areal recording density necessitate further development of high bit density magnetic recording media, e.g., perpendicular-type media.
Accordingly, the use of lower cost materials, e.g., polymers, glass, ceramics, and glass-ceramic composite materials, as replacements for the conventional Al alloy-based substrates for magnetic disk media has been proposed. However, only materials such as glass, glass-ceramic composite materials, and high cost, high temperature-resistant polymer materials which are capable of withstanding the elevated temperatures to which the substrates are subjected during conventional manufacturing processing for depositing the various constituent layers of the media (e.g., high temperature sputter deposition of the magnetic recording layer(s)), have been successfully utilized for the manufacture of practical disk media. Of these candidate substrate materials, the extreme difficulty associated with grinding and lapping of glass and glass-ceramic composite materials have limited their use to higher cost applications, such as mobile disk drives for “notebook” type computers, and the high cost of the high temperature-resistant polymer materials renders them unsuitable for lower cost disk drive applications.
In view of the foregoing, there exists a need for improved, lower cost high areal recording density perpendicular magnetic recording media utilizing low cost, readily available polymer substrate materials, and methodology for manufacturing same. In addition, there exists a need for improved, lower cost hard disk drives and systems including the lower cost polymer substrate-based magnetic recording media.
The present invention addresses and solves problems attendant upon the design and manufacture of lower cost, high recording density, high performance perpendicular magnetic recording media and disk drive systems incorporating same, while maintaining full compatibility with all aspects of conventional disk drive technology and manufacturing processing. Moreover, the present invention enables the manufacture of such hard disk media and disk drive systems at significantly reduced cost, relative to conventional technology and methodology, thereby contributing substantially toward achieving the aim of manufacture of very low cost computers.